connecting two totem pole outputs together

An emitter follower, is either a single device, as shown in 'A'. Here is a simple low power fairly low distortion audio amplifier using boot strapped dynamic biasing.Īs for emitter follower vs darlington. Totem pole output circuits were also later used in TTL logic ICs because of the low saturation voltage in the Logic '0' state. Totem pole output circuits were common in very early power transistor audio amplifiers. This technique is know as 'boot strapping' as in the old saying 'pulling yourself up by your boot straps'.Ī totem pole amplifier uses two devices of the same type, either PNP or NPN, one of which is driven by a phase inverter device. These resistors are added to allow a higher output with a given power supply voltage, by keeping the voltage across the bias circuit more or less constant as higher AC output voltages approach the power supply rails. In 'E' resistors are added in series with the bias transistor, and capacitors coupled to the output. To minimize thermal considerations the bias transistor can be mounted on the heat sink along with the output power devices. Idle current and distortion can be well controlled by using dynamic biasing with an additional transistor, as shown in 'D' and 'E'. Because of differences in each transistor, resistors must be hand selected, not good for mass production.

This works better, but there can still be cross over distortion and or Idle current problems, which can be reduced by inserting additional resistors as shown in'C'. One is to stack diodes in the base circuit to parallel the B-E junctions in the transistors as shown in 'B'. To improve crossover distortion, a couple basic approaches can be used.

As shown at 'A' the circuit will have considerable crossover distortion at low volume settings, thus, is not well suited to audio amplifier amplifiers.

The OP's circuit is a particular type of push-pull amplifier, known as a complimentary symmetry current amplifier, so named because it uses a complimentary pair of PNP and an NPN devices, in an Emitter follower configuration. This circuit was quite popular in descrete power amplifiers of the 70s and 80s. This will allow you to easily set the Idle current (no signal) and very significantly reduce crossover distortion. THe best solution is to use a dynamic bias circuit.

Connecting two totem pole outputs together